Monitoring: pulse oximetry: practice question

A Anaesthesia question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anaesthesia · Monitoring: pulse oximetry

Sample item

Pulse oximetry may appear reassuring in a carbon-monoxide-poisoned patient because it cannot reliably distinguish what?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Oxyhaemoglobin from carboxyhaemoglobin

Standard two-wavelength pulse oximetry can misread carboxyhaemoglobin as oxyhaemoglobin. Co-oximetry is required when carbon monoxide poisoning is suspected.

Option by option

  • A. Arterial from venous pressure

    Pulse oximetry does not measure pressure.

  • B. Inspired from expired carbon dioxide

    Capnography, not oximetry, compares inspired and expired carbon dioxide.

  • C. Sodium from potassium

    It does not identify electrolytes.

  • D. Oxyhaemoglobin from carboxyhaemoglobin (correct)

    Correct. Dyshemoglobins confound conventional pulse oximetry.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is D, Oxyhaemoglobin from carboxyhaemoglobin. Standard two-wavelength pulse oximetry can misread carboxyhaemoglobin as oxyhaemoglobin.

Why is "Arterial from venous pressure" not the answer?

Pulse oximetry does not measure pressure.

Why is "Inspired from expired carbon dioxide" not the answer?

Capnography, not oximetry, compares inspired and expired carbon dioxide.

Why is "Sodium from potassium" not the answer?

It does not identify electrolytes.

What concept does this question test?

It tests Monitoring: pulse oximetry in Anaesthesia. Co-oximetry is required when carbon monoxide poisoning is suspected.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Monitoring: pulse oximetry?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.